Green Party MP Keith Locke has failed in his bid to let New Zealanders decide whether they want to keep a British monarch as head of state or elect their own non-executive president.

Mr Locke's member's bill, debated in Parliament last night, would have set up a referendum but it didn't have enough support to get through its first reading.

The Head of State Referenda Bill was defeated 68-53. National, ACT, the Maori Party and the Progressive Party opposed it. Labour supported sending it to a select committee and it was also backed by the Greens and United Future.

Mr Locke said that under the terms of his bill an elected head of state would not have different powers to those held by the present Governor-General, and described his proposal as "minimal change".

"The question many New Zealanders ask is: why should we have a head of state on the other side of the world who is not a citizen of our country?" he said.

"There is also concern about whether our head of state should remain a monarch - that is somebody who inherits the job rather than getting it through a democratic process."

He said some people feared New Zealand would end up with a pop star, a celebrity or a political hack as president but he didn't think that would happen.

"I believe we should trust Kiwis to vote responsibly for such an important position," he said.

"Ireland has a directly elected president with minimal powers like those proposed in my bill, and the Irish people have elected appropriate heads of state like the internationally renowned Mary Robinson."

Mr Locke's bill would have set up two referenda - the first to decide whether voters wanted a change and the second to decide a process for electing a head of state.

National MP Simon Bridges said his party opposed the bill and he personally wasn't much concerned about the issue.

"There are much more important things to deal with," he said.

"Over time we might look seriously at becoming a republic but now is not the time. It would be a distraction."

Labour's Charles Chauvel said the bill should go to a select committee so there could be a public discussion.

"Tonight isn't going to see the start of the republican journey, but the day surely doesn't lie far ahead," he said.

Maori Party MP Rahue Katene said the bill had the potential to make Maori's relationship with the Crown obsolete.

Speaking in reply to the debate, Mr Locke said his bill would have had a majority if the Government had allowed its MPs to have a free vote.